Added beta variations

FastRng/Double/Distributions/BetaA2B5.cs

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+using System;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace FastRng.Double.Distributions
+{
+    public sealed class BetaA2B5 : IDistribution
+    {
+        private const double ALPHA = 2;
+        private const double BETA = 5;
+        private const double CONSTANT = 12.2;
+        
+        private ShapeFitter fitter;
+        private IRandom random;
+
+        public BetaA2B5()
+        {
+        }
+        
+        public IRandom Random
+        {
+            get => this.random;
+            set
+            {
+                this.random = value;
+                this.fitter = new ShapeFitter(BetaA2B5.ShapeFunction, this.random, 100);
+            }
+        }
+
+        private static double ShapeFunction(double x) => CONSTANT * Math.Pow(x, ALPHA - 1) * Math.Pow(1 - x, BETA - 1);
+
+        public async ValueTask<double> GetDistributedValue(CancellationToken token = default)
+        {
+            if (this.Random == null)
+                return double.NaN;
+            
+            return await this.fitter.NextNumber(token);
+        }
+    }
+}

FastRng/Double/Distributions/BetaA5B2.cs

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+using System;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace FastRng.Double.Distributions
+{
+    public sealed class BetaA5B2 : IDistribution
+    {
+        private const double ALPHA = 5;
+        private const double BETA = 2;
+        private const double CONSTANT = 12.2;
+        
+        private ShapeFitter fitter;
+        private IRandom random;
+
+        public BetaA5B2()
+        {
+        }
+        
+        public IRandom Random
+        {
+            get => this.random;
+            set
+            {
+                this.random = value;
+                this.fitter = new ShapeFitter(BetaA5B2.ShapeFunction, this.random, 100);
+            }
+        }
+
+        private static double ShapeFunction(double x) => CONSTANT * Math.Pow(x, ALPHA - 1) * Math.Pow(1 - x, BETA - 1);
+
+        public async ValueTask<double> GetDistributedValue(CancellationToken token = default)
+        {
+            if (this.Random == null)
+                return double.NaN;
+            
+            return await this.fitter.NextNumber(token);
+        }
+    }
+}

FastRngTests/Double/Distributions/BetaA2B5.cs

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+using System;
+using System.Diagnostics.CodeAnalysis;
+using System.Linq;
+using System.Threading.Tasks;
+using FastRng.Double;
+using NUnit.Framework;
+
+namespace FastRngTests.Double.Distributions
+{
+    [ExcludeFromCodeCoverage]
+    public class BetaA2B5
+    {
+        [Test]
+        [Category(TestCategories.COVER)]
+        [Category(TestCategories.NORMAL)]
+        public async Task TestBetaDistribution01()
+        {
+            var dist = new FastRng.Double.Distributions.BetaA2B5();
+            var fqa = new FrequencyAnalysis();
+            var rng = new MultiThreadedRng();
+            
+            for (var n = 0; n < 100_000; n++)
+                fqa.CountThis(await rng.NextNumber(dist));
+            
+            rng.StopProducer();
+            var result = fqa.NormalizeAndPlotEvents(TestContext.WriteLine);
+            
+            Assert.That(result[0], Is.EqualTo(0.11719271).Within(0.3));
+            Assert.That(result[1], Is.EqualTo(0.22505783).Within(0.3));
+            Assert.That(result[2], Is.EqualTo(0.32401717).Within(0.3));
+            
+            Assert.That(result[21], Is.EqualTo(0.99348410).Within(0.3));
+            Assert.That(result[22], Is.EqualTo(0.98639433).Within(0.3));
+            Assert.That(result[23], Is.EqualTo(0.97684451).Within(0.3));
+            
+            Assert.That(result[50], Is.EqualTo(0.35868592).Within(0.3));
+            
+            Assert.That(result[75], Is.EqualTo(0.03076227).Within(0.03));
+            Assert.That(result[85], Is.EqualTo(0.00403061).Within(0.03));
+            Assert.That(result[90], Is.EqualTo(0.00109800).Within(0.01));
+            
+            Assert.That(result[97], Is.EqualTo(0.00000191).Within(0.000003));
+            Assert.That(result[98], Is.EqualTo(0.00000012).Within(0.0000003));
+            Assert.That(result[99], Is.EqualTo(0.00000000).Within(0.0000003));
+        }
+    }
+}

FastRngTests/Double/Distributions/BetaA5B2.cs

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+using System;
+using System.Diagnostics.CodeAnalysis;
+using System.Linq;
+using System.Threading.Tasks;
+using FastRng.Double;
+using NUnit.Framework;
+
+namespace FastRngTests.Double.Distributions
+{
+    [ExcludeFromCodeCoverage]
+    public class BetaA5B2
+    {
+        [Test]
+        [Category(TestCategories.COVER)]
+        [Category(TestCategories.NORMAL)]
+        public async Task TestBetaDistribution01()
+        {
+            var dist = new FastRng.Double.Distributions.BetaA5B2();
+            var fqa = new FrequencyAnalysis();
+            var rng = new MultiThreadedRng();
+            
+            for (var n = 0; n < 100_000; n++)
+                fqa.CountThis(await rng.NextNumber(dist));
+            
+            rng.StopProducer();
+            var result = fqa.NormalizeAndPlotEvents(TestContext.WriteLine);
+            
+            Assert.That(result[0], Is.EqualTo(0.0000001).Within(0.0000003));
+            Assert.That(result[1], Is.EqualTo(0.0000019).Within(0.0000020));
+            Assert.That(result[2], Is.EqualTo(0.0000096).Within(0.0000100));
+            
+            Assert.That(result[21], Is.EqualTo(0.0222918).Within(0.03));
+            Assert.That(result[22], Is.EqualTo(0.0262883).Within(0.03));
+            Assert.That(result[23], Is.EqualTo(0.0307623).Within(0.03));
+            
+            Assert.That(result[50], Is.EqualTo(0.4044237).Within(0.2));
+            
+            Assert.That(result[75], Is.EqualTo(0.9768445).Within(0.03));
+            Assert.That(result[85], Is.EqualTo(0.9552714).Within(0.05));
+            Assert.That(result[90], Is.EqualTo(0.8004420).Within(0.15));
+            
+            Assert.That(result[97], Is.EqualTo(0.2250578).Within(0.03));
+            Assert.That(result[98], Is.EqualTo(0.1171927).Within(0.03));
+            Assert.That(result[99], Is.EqualTo(0.0000000).Within(0.00));
+        }
+    }
+}